Anode assembly for electrolytic cells

ABSTRACT

An anode assembly for electrolytic cells comprising: a downwardly-facing, open-ended, horizontally-elongated titanium channel member having a web portion and two depending flange portions integral with the web portion; a titanium tube secured at one end to said web portion in a fluid-tight manner so that said web portion closes said end, said web portion having at least one gas escape opening therethrough located intermediate said tube and each end of said channel an aluminum current leadin rod at least partially within the tube coaxially therewith having one end friction-welded to said web portion; and a foraminate titanium structure lying in a plane parallel to said web portion and electrically connected to the lower edges of the flange portions, said foraminate structure carrying on at least a part of its surface a coating comprising an operative electrode material.

United States Patent Smith et al. 51 July 11, 1972 54 ANODE ASSEMBLY FOR3,318,792 5/1967 Cotton et al ..204/290 F ELECTROLYTIC CELLS 3,458,4237/ 1969 Csizi 20 M290 F 3,437,579 4/1969 Smith ..204/288 [72] Inventors:Frank Smith; John Hubert Entwisle, both of Runcorn, England FOREIGNPATENTS OR APPLICATIONS [73] Assignee: Imperial Chemical IndustriesLimited, 668,618 9/1950 Great Britain ..204/284 London, England 453,75012/1927 Germany ..204/284 [22] Filed: June 1970 Primary Examiner-John H.Mack Assistant ExaminerRegan J. Fay Attorney-Cushman, Darby & Cushman[30] Foreign Application Priority Data [57] ABSTRACT June 27, 1969 GreatBritain ..32,544/69 An anode assembly for electrolytic cells comprising:a downwardly-facing, openended, horizontally-elongated [52] US. Cl..204/288, 204/219, 204/250, titanium channel member having a webportion and two de- 204/284, 204/286, 204/290 F pending flange portionsintegral with the web portion; a titani- [51] Int. Cl..... ..B01k 3/04,C23g 5/68, B01r 3/04 um tube secured at one end to said web portion in afluid-tight [58] Field of Search ..204/288, 28l, 29 F, 290 R, manner 80that Said Web Portion Closes Said end, Said Web P 204 219 250 tionhaving at least one gas escape opening therethrough located intermediatesaid tube and each end of said channel [56] R fe e Cited an aluminumcurrent lead-in rod at least partially within the tube coaxiallytherewith having one end friction-welded to UNITED STATES PATENTS saidweb portion; and a foraminate titanium structure lying in a planeparallel to said web portion and electrically connected 3,297,561 1/1967Harrison et al. ..204/29OF to the lower edges of the flange ponions,Said foraminate 3409533 11/1968 '"204/221 X structure carrying on atleast a part of its surface a coating 3,455,810 7/1969 Holm ..204/250 XComprising an operative electrode material 3,511,766 5/1970 Klsner eta1. ..204/286 X 3,271,289 9/1966 Messner ..204/219 14 Claims, 7 DrawingFigures PA'TENTEDJUL 11 I972 3, 676.325

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/ z r /vz/s M ANODE ASSEMBLY FOR ELECTROLYTIC CELLS The presentinvention relates to an anode assembly for electrolytic cells. Moreparticularly it relates to an anode assembly which is particularlysuitable for use in cells where gas is evolved at the anode.

In recent years it has been proposed to employ as anodes, particularlyin cells electrolyzing aqueous alkali metal chloride solutions,structures in which a layer of a platinum group metal or metals and/orthe oxides thereof constitutes the working anode surface and is carriedon a support made of a film-forming metal, usually titanium. The anodeconductor leading the current to the anode within the cell may also beconstructed of titanium since this metal is resistant to electrochemicalattack under the severe anodic conditions ruling in the cell, but inorder to reduce capital expenditure and running costs it is desirable touse as far as possible a cheaper and better conducting metal. It hastherefore been proposed to use as the current lead-in a compositestructure in which a core of copper, steel or aluminum is protected fromelectrochemical attack by a casing or sheath of titanium. Aluminum isgenerally the most desirable core metal on the basis of cost/weight foradequate electrical conductivity but such a structure presents theproblem of making a mechanically strong and low-resistance electricalconnection between the aluminum core and the titanium of the casing orthe titanium support member of the anode structure. This is importantbecause the current carried principally by the good-conducting aluminumcore must pass in some region across an interface between the aluminumof the core and the titanium of the casing or the anode structure itselfin order to reach the working anode surface. I

it has been proposed to solve this problem by melting and alloying analuminum core inside a titanium casing and by soldering an aluminum coreinto a titanium casing after coating the juxtaposed surfaces of the coreand casing with a solderable metal. Melting and alloying is a hightemperature process which can cause distortion. Soldering introducesproblems of shrinkage between the core and the casing on cooling and isexpensive in labor because of the pre-coating operations that areneeded.

The present invention overcomes these problems by providing afriction-welded joint between an aluminum current leadin and a titaniummember which supports the anode structure proper. Other advantageousfeatures of the invention will appear hereinafter.

According to the present invention we provide an anode assembly forelectrolytic cells which comprises a titanium tube having a flattitanium closure attached in fluid-tight manner across one end, analuminum current lead-in at least partially within the tube and coaxialtherewith having one end frictionwelded to the titanium closure, and aforaminate titanium structure carrying on at least a part of its surfacea coating comprising an operative electrode material, the saidforaminate titanium structure lying in a plane parallel to the saidtitanium closure and being electrically connected thereto by titaniummembers which together with the said closure define an inverted channelshape.

in this specification by titanium" we mean titanium alone or an alloybased on titanium and having anodic polarization properties comparableto those of titanium.

The operative electrode material may be any material which is active intransferring electrons from an electrolyte to the underlying titaniumstructure of the anode assembly and which is resistant toelectrochemical attack under the conditions ruling in the cell where theanode is to be used. For use in very corrosive media, for instance inchloride electrolytes, the operative electrode material may suitablyconsist of one or more platinum group metals i.e. platinum, rhodium,iridium, ruthenium, osmium and palladium, and/or oxides thereof, oranother metal or a compound which will function as an anode and which isresistant to electrochemical dissolution in the cell, for instancerhenium, rhenium trioxide, magnetite, titanium nitride, the borides,phosphides or silicides of the platinum group metals, or an oxidicsemiconducting compound. The

coating comprising an operative electrode material may also containelectronically non-conducting oxides, particularly oxides of thefilm-forming metals such as titanium, as is known in the art, to anchorthe operative electrode material more securely to the supportingtitanium structure and to increase its resistance to dissolution in theworking cell. A preferred coating comprising an operative electrodematerial for anodes that are to be used in mercury-cathode cellselectrolyzing alkali metal chloride solutions consists of at least oneoxide of at least one platinum group metal, particularly rutheniumdioxide, as the operative electrode material, and titanium dioxide.

When ananode assembly according to the invention is installed in a cell,the titanium tube passes through sealing means in thecell casing, forinstance the cover of the cell, so that the aluminum current lead-in rodis protected from contact with the cell contents. In general thealuminum current lead-in rod is made of sufficient length to protrudefrom the titanium tube for easy connection of an electrical bus-bar tothe end of the rod outside the cell.

In preferred embodiments of the invention the titanium closure and thetitanium members together defining an inverted channel shape arefabricated from one integral piece of titanium metal. Furthermore, theinverted channel shape may extend both laterallyand longitudinally wellbeyond the limits defined by the cross-section of the end of thetitanium tube to which the base of the channel forms a closure, andusually will so extend, in order to support a coated foraminate titaniumstructure of sufficient area to provide the desired working anode areawhen installed in the cell. Such embodiments are illustrated in theaccompanying drawings FlG. 1-7, which are not to scale and in which likeparts are numbered alike.

FIG. 1 and FIG. 2 show vertical sections at right angles to each otherthrough the center of an electrode assembly. In these figures the centerpart of an inverted titanium channel 1 forms a fluid-tight closureacross the lower end of titanium tube 2 by virtue of a peripheral weldaround the end of the tube indicated as 3. (Other suitable forms, notshown, for the weld 3 are electrical resistance welding and frictionwelding). An aluminum current lead-in rod 4 has its lower end attachedto the center of the channel 1 by a friction weld indicated at 5. Theedges of the channel 1 are welded at intervals as indicated at 6 to ahorizontally-disposed foraminate titanium structure 7 which carries onat least a part of its surface a coating (not shown) comprising anoperative electrode material as defined hereinbefore. The foraminatetitanium structure 7 may suitably be a multi-holed titanium sheet, forinstance a sheet of expanded titanium metal. Alternatively theforaminate structure may be built up from longitudinally-extendedtitanium members spaced apart with their long axes parallel to eachother, each one being welded to both bottom edges of the invertedchannel. These members may be for instance flat strips. rods,hemicylindrical channels which are convex upwards or convex downwards orchannels of U-shaped or inverted U- shaped, the closed end of the Ubeing optionally flattened. Yet again, an arrangement approximating tothe said built-up structure of longitudinally-extending members spacedapart with their long axes parallel to each other may be produced bypressing from a titanium sheet by means of a slotting and forming tool,whereby a structure with pressed-out louvres is obtained. The. louvreslats so obtained may suitably be turned at right angles to the originalplane of the titanium sheet or they mayhave each of their edges rolledround to form approximately hemicylindrical members which alternate withthe slots from which the metal forming them has been pressed out. FIG. 3shows an anode assembly in which the foraminate titanium structure isbuilt up from parallel-spaced titanium strips 8, which each have onelong edge welded to both bottom edges of the inverted titanium channel 1as again indicated at 6. The other parts of FIG. 3 correspond to thoseof FIG. 2. When the foraminate titanium structure is built up in thismanner, at least half of the coating thereon comprising an operativeelectrode material may suitably be carried on the faces of the strips 8(the vertical surfaces in the configuration in the drawing), as taughtfor instance in British Patent Specification No. 1,076,973 for coatingsof the platinum group metals on anode surfaces formed from titaniumribs.

If desired, within the scope of the invention the titanium tube whichsurrounds the aluminum current lead-in may be provided with a flange atits lower end, the fluid-tight joint between the titanium tube and theinverted titanium channel then being made by welding the flange to thechannel. Likewise each of the sides of the inverted channel may beterminated by a flange, the foraminate titanium structure carrying thecoating comprising an operative electrode material then being welded tothese flanges. An anode assembly incorporating these optional featuresis illustrated in FIG. 4, with the flange 8 and weld 9 replacing theweld 3 of FIG. 1 and the flanges l and welds ll replacing the welds 6 ofFIG. 1.

In FIG. 1-4 the aluminum current lead-in rod 4 is shown substantiallyfilling the cross-section of titanium tube 2. In general we prefer thisarrangement, in which only sufficient clearance is provided between therod and the tube for easy assembly of these parts, so as to obtain thelowest electrical resistance in the aluminum rod commensurate with thediameter of the tube employed. It is not, however, essential for the rodto be a close fit within the tube and a wider gap may be providedbetween these two members if desired.

An anode assembly according to the invention is very suitable for use ina cell wherein gas is evolved at the anode, with the working anodestructure of coated foraminate titanium arranged parallel to asubstantially horizontal cathode, e.g. a flowing mercury cathode, sincegas evolved beneath the current lead-in can pass freely upwards throughthe foraminate structure into the space beneath the inverted titaniumchannel. The gas may be allowed to flow out from under the ends of theinverted channel or, if desired, one or more openings to assist theescape of gas may be provided in the top of the channel between thecentrally disposed titanium tube and each end of the channel. Suitablearrangements of opening are shown in FIG. 57, which are plan viewsshowing only the titanium channel-shaped member 1 and the current leadin 4 with its surrounding titanium tube 2. In the arrangement of FIG. 5there is one large opening 12 provided towards each end of the channel.In the arrangement of FIG. 6 there is a plurality of small openings 13towards each end of the channel and in the arrangement of FIG. 7 thechannel is cut away at each end in approximately a V-shape 14 to assistthe escape of gas.

What we claim is:

1. An anode assembly for electrolytic cells which comprises a titaniumtube having a fiat titanium closure attached in fluidtight manner acrossone end, an aluminum current lead-in rod at least partially within thetube and coaxial therewith having one end friction-welded to thetitanium closure, and a foraminate titanium structure carrying on atleast a part of its surface a coating comprising an operative electrodematerial, the said foraminate titanium structure lying in a planeparallel to the said titanium closure and being electrically connectedthereto by titanium members which together with the said closure definean inverted channel shape.

2. An anode assembly according to claim 1, wherein the said titaniummembers and the titanium closure which together define an invertedchannel shape have been fabricated from one integral piece of titaniummetal.

3. An anode assembly according to claim 1, wherein the edges of thetitanium channel shape are welded at intervals to the foraminatetitanium structure.

4. An anode assembly according to claim 1, wherein the foraminatetitanium structure is a sheet of expanded titanium metal.

5. An anode assembly according to claim 1, wherein the foraminatetitanium structure has been built up from longitudinally-extendingtitanium members spaced apart with their long axes parallel to eachother.

6. An anode assembly according to claim 5, wherein thelongitudinally-extending titanium members are flat strips which eachhave one long edge welded to the edges of the titanium channel shatlge.

7. An anode assem ly according to claim 6, wherein at least half thecoating comprising an operative electrode material is carried on thefaces of the said flat strips.

8. An'anode assembly according to claim 1, wherein the foraminatetitanium structure is louvred structure formed by pressing a series ofof louvre slats from a titanium sheet.

9. An anode assembly according to claim 8, wherein the louvre slats havebeen turned at right angles to the original plane of the titanium sheet.

10. An anode assembly according to claim 1, wherein the foraminatetitanium structure comprises a titanium sheet having a plurality oflouvre slats pressed out so as to form a plurality of correspondingslots, the slats having rolled edges so as to form a series ofapproximately hemicylindrical members which alternate with the slots.

11. An anode assembly according to claim 1, wherein the operativeelectrode material in selected from the group consisting of platinumgroup metals and oxides thereof.

12. An anode assembly according to claim 1, wherein the coatingcomprising an operative electrode material consists of at least oneoxide of at least one platinum group metal as the operative electrodematerial and titanium dioxide.

13. An anode assembly according to claim 12, wherein the said operativeelectrode material is ruthenium dioxide.

14. An anode assembly for electrolytic cells comprising:

a downwardly-facing, open-ended, horizontally-elongated titanium channelmember having a web portion and two depending flange portions integralwith the web portion;

a titanium tube secured at one end to said web portion in a fluid-tightmanner so that said web portion closes said end, said web portion havingat least one gas escape opening therethrough located intermediate saidtube and each end of said channel;

an aluminum current lead-in rod at least partially within the tubecoaxially therewith having one end friction-welded to said web portion;and

a foraminate titanium structure lying in a plane parallel to said webportion and electrically connected to the lower edges of the flangeportions, said foraminate structure carrying on at least a part of itssurface a coating comprising an operative electrode material.

2. An anode assembly according to claim 1, wherein the said titaniummembers and the titanium closure which together define an invertedchannel shape have been fabricated from one integral piece of titaniummetal.
 3. An anode assembly according to claim 1, wherein the edges ofthe titanium channel shape are welded at intervals to the foraminatetitanium structure.
 4. An anode assembly according to claim 1, whereinthe foraminate titanium structure is a sheet of expanded titanium metal.5. An anode assembly according to claim 1, wherein the foraminatetitanium structure has been built up from longitudinally-extendingtitanium members spaced apart with their long axes parallel to eachother.
 6. An anode assembly according to claim 5, wherein thelongitudinally-extending titanium members are flat strips which eachhave one long edge welded to the edges of the titanium channel shape. 7.An anode assembly according to claim 6, wherein at least half thecoating comprising an operative electrode material is carried on thefaces of the said flat strips.
 8. An anode assembly according to claim1, wherein the foraminate titanium structure is louvred structure formedby pressing a series of of louvre slats from a titanium sheet.
 9. Ananode assembly according to claim 8, wherein the louvre slats have beenturned at right angles to the original plane of the titanium sheet. 10.An anode assembly according to claim 1, wherein the foraminate titaniumstructure comprises a titanium sheet having a plurality of louvre slatspressed out so as to form a plurality of corresponding slots, the slatshaving rolled edges so as to form a series of approximatelyhemicylindrical members which alternate with the slots.
 11. An anodeassembly according to claim 1, wherein the operative electrode materialin selected from the group consisting of platinum group metals andoxides thereof.
 12. An anode assembly according to claim 1, wherein thecoating comprising an operative electrode material consists of at leastone oxide of at least one platinum group metal as the operativeelectrode material and titanium dioxide.
 13. An anode assembly accordingto claim 12, wherein the said operative electrode material is rutheniumdioxide.
 14. An anodE assembly for electrolytic cells comprising: adownwardly-facing, open-ended, horizontally-elongated titanium channelmember having a web portion and two depending flange portions integralwith the web portion; a titanium tube secured at one end to said webportion in a fluid-tight manner so that said web portion closes saidend, said web portion having at least one gas escape openingtherethrough located intermediate said tube and each end of saidchannel; an aluminum current lead-in rod at least partially within thetube coaxially therewith having one end friction-welded to said webportion; and a foraminate titanium structure lying in a plane parallelto said web portion and electrically connected to the lower edges of theflange portions, said foraminate structure carrying on at least a partof its surface a coating comprising an operative electrode material.